Shooting 40 S&w In A 10mm Kimber

The one and only mag that came with this handgun will not accept factory
10 mm loads. The OAL is too long so as you load it up the ammo binds up in the magazine
preventing it from feeding. Has Kimber mis-marked any single stack 40 mags or is this just a freak quality glitch. Also what damage can be done if I do shoot 40's out of this gun.
Thanks Jed B.

Hey Jed, A friend shot some .40's out of a 10mm Delta I believe and it didn't cycle well and really funked up the primers. The .40 uses small pistol primers, the 10mm use large pistol primers. I wouldn't recommend shooting them. Mac

The reason for the ugly primers is that the case is "headspacing" on the extractor and not the barrel.

The firing pin drives the case forward, as far as the extractor will let it go, before the primer ignites and then the case slams back into the breechface (crushing the primer) as the round goes off. The primers can look similar to a case with extreme pressure problems, although that is not usually the case.

Jeb, First of all, don't shoot .40 Cal in a 10 MM barrel. These rounds headspace on the empty cartridge length, not the overall length of the loaded round. Putting a .40 in a 10mm means that the round is not properly supported in the chamber and would be dangerous.

I have been shooting 10mm and .40's for a while and leanded a couple important lessons about feeding, magazines and power factors. First, I found that .40 cal rounds at factory length don't feed 100 percent in 1911 geometry guns including SV and STi's. The round is just a little shot and tends to hang up occasionaly. Secondly, a 10mm round feeds well in the same type of guns but binds in the magazine. Espicially true of fat nosed bullets (180 gr or above).

I have fixed both problemas by loading my .40 cal rounds long (1.220 OAL) and my 10mm rounds short (1.25 OAL.) I have absolutely no problems with case feed failures or being able to load magazines to full capacity. (Note: this only applies to 1911 style guns). My 10mm loads are loaded with 135gr Nosler JHP's and I load my .40 with Zero 180gr JHP. You might have to work loads up since the long loads will have decreased pressure and the shortened 10mm loads will have increased pressure.

There was a thread on 10mm conversions on another forum. [Going the other way. P-16/40 to 10 mm] The comment was that the OAL for each caliber was very significant. I believe the gent who had the most knowledgeable comments was Bob Hunter from Hunter Custom Guns. Might be helpful to reference information on his web site regarding the conversions and possible OAL loading considerations.

On a parallel note, I've launched a few 40 SW out of my Glock 20 (10mm) successfully. I was simply verifying that it could be done, not advised for the reasons already posted on head spacing. I did not experience any issues with primer deformation in my very limited testing. I did purchase a conversion barrel which allows me to shoot 40 SW with the proper chamber support. It is one of my preferred setups for go fast mode. So far the only slight negative I've found is that with the shorter 40 SW rounds don't always sit to the rear of the magazine which makes limited use of the witness/index holes. Just have to look extra close to see how many rounds are on board the magazines when setting up in between stages.

Best of luck to ya. Cheers!

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